1. Field of the Invention
The present invention relates to a vibration compensation device for a camera which corrects image blur caused by, for example, hand vibration, and in particular, relates to a camera having a vibration compensation device that provides a visual indication of the presence of vibrations and presents the user with the same sense of timing when taking a picture while using the vibration compensation device as when taking a picture without using the vibration compensation device.
2. Description of the Related Art
In known cameras having a vibration compensation device using a vibration compensation detection sensor to detect vibrations which may cause image blur, only information related to exposure and the shutter speed has heretofore been displayed to the photographer to assist in determining whether a suitable photograph can be produced. However, even if the exposure and shutter speed are suitable for photography, vibrations in the camera can still produce an unsuitable photograph, i.e. if the photographer takes a picture when there is too much vibration, the photograph is wasted.
This situation is compounded in recent cameras which are remarkably lighter and more prone to vibration than prior cameras. The photographer may not notice the weight of the camera even when taking photographs for a long period of time. As the cameras have become lighter, more and more blurred photographs are produced in which the subject image is a vibrating locus, due to, for example, vibrations in the hand of the photographer. Moreover, in situations which call for the use of a slow shutter speed, due to, for example, the brightness of the subject, the sensitivity of the film used, and the aperture of the lens being used, the photographer needs to prevent vibration in order to produce an acceptable photograph. This can be accomplished by extensive practice at holding the camera still, installing the camera on a tripod, raising the sensitivity of the film used, using a lens with a larger aperture, and/or using a vibration compensation device.
Known vibration compensation devices use an angular velocity sensor, as a vibration detection unit, incorporated into the camera body or a photographic lens. When positioned in the camera body, the angular velocity sensor detects the vibration in the camera body, or photographic lens, and outputs a signal indicative of the detected vibrations. A computational unit, incorporated into the camera, uses the signal to compute the amount and the direction of movement of a subject image on a focal plane, that is, on a photographic screen of the photographic film, caused by the vibration. Further, the angular velocity sensor may also output the relative detection value of how much change occurs from a given detection value to a next detection value. When computing the amount and direction of movement of the subject image using the relative detection value, the computational unit executes computations to convert the relative detection value to an absolute amount of movement from a standard value where angular velocity equals 0. Based on the computations, a vibration compensation unit, typically comprising an actuator, incorporated into the photographic lens and capable of driving one part of a photographic optical system in a direction perpendicular to the optical axis of the photographic optical system, drives one part of the photographic optical system so as to cancel out the amount of movement of the subject image. These operations are typically initiated by manipulating a shutter release button, usually by pressing the shutter release button halfway. These known vibration compensation devices reduce the vibration of the subject image on the photographic screen during exposure.
The signal output from the angular velocity sensor immediately after initiating vibration detection lacks reliability because the angular velocity sensor has not entered a stable state. It is therefore necessary to begin computations, by determining the point where the angular velocity equals 0, after enough time has elapsed for the output of the angular velocity sensor to become stable. Angular velocity is said to equal 0 at a point equal to the average value of the detection values as measured within a set time period starting from just after the beginning of vibration detection. The set time period is equal to the time required for the detection output of the angular velocity sensor to become stable plus the time required to calculate where the angular velocity equals 0. The time required in order to calculate where the angular velocity equals 0 is determined by the time it takes the computational unit to compute the amount and direction of motion of the subject image. A longer set time period allows more angular velocity detection values to be measured, which gives a higher precision in calculating the points where the angular velocity equals 0. However, if the set time period becomes too long, then difficulty arises in taking the photograph. Moreover, if the set time period is too short, the precision of determining the point where the angular velocity equals 0 is lowered.
Thus, the time required for the series of operations accompanying the operation of the shutter release button until exposure of the photographic screen can begin (hereinafter referred to as "release time lag") takes longer when a vibration compensation unit is used because of the extra calculations. This can cause problems when a photographer attempts to take a photograph of a moving subject while using the vibration compensation device. As the release time lag is not the same as when taking a photograph without using the vibration compensation device, it is difficult to determine the best time for operating the shutter release button, and the sensation of pressing the shutter release button changes completely. Therefore, not only is it difficult to obtain the photograph as intended, but it is typically necessary to conduct photography several times until a satisfactory photograph is obtained, due to the different timing of the shutter release operation, i.e. differences in the release lag time. This presents an obstacle to the photographer when taking photographs while using the vibration compensation device.